Planar contact array switch having improved ground path for dissipating electrostatic discharges

Abstract

An improved planar contact array switch having reduced susceptibility to electrostatic discharge includes a printed circuit board which carries at least one switch contact foil pair. Sandwiched between the circuit board and an insulative overlay is a dome-shaped disc which, when depressed, completes an electrical circuit between the switch contact foil pair. Bordering the periphery of the printed circuit board so as to bound the area occupied by each of the switch contact foil pair is a ground foil which advantageously is provided with at least one inwardly extending charge conductive foil which runs adjacent to each of the switch contact foil pairs for conducting any electrostatic discharge which penetrates the overlay within the area bordered by the ground foil. To facilitate the conduction of electrostatic discharges to the perimeter ground foil through the charge conductive foil, a spark gap is provided between each of the switch contact foil pairs and the charge conductive foil so that an electrostatic discharge may jump the spark gap and be conducted via the charge conductive foil on the ground plane to circuit ground.

What is claimed is: 
     
       1. An improved switch comprising: a substrate having a first surface which embodies a perimeter ground path thereon and at least one switch contact path laterally spaced from said ground path;   a conductive member overlying said switch contact path but only making electrical contact therewith to complete an electrical circuit therewith when said conductive member is urged against said switch contact path; and   at least one charge conductive path on said first surface of said substrate so as to extend from said ground path adjacent to said switch contact path for carrying any electrostatic discharge impacting said substrate adjacent to said switch contact path away from said switch contact path to said ground path.   
     
     
       2. The invention according to claim 1 further including an insulative overlay secured to said surface of said substrate to overlie said conductive member so that said conductive member is sandwiched between said overlay and said first surface of said substrate. 
     
     
       3. The invention according to claim 1 further including a conductive spike path extending from said switch contact path towards said charge conductive path and a conductive spike path extending from said charge conductive path towards said conductive spike extending from said switch contact path so as to form a spark gap therebetween to enable an electrostatic discharge to jump said spark gap and to be carried along said charge conductive path to said ground path. 
     
     
       4. The invention according to claim 1 wherein said substrate carries a radio frequency interference shield on its surface opposing said first surface. 
     
     
       5. The invention according to claim 1 wherein said substrate carries a plurality of switch contact paths arranged in a matrix array of C columns by R rows and wherein said substrate carries a plurality of charge conductive paths, each charge conductive path extending from said ground plane between an adjacent pair of columns of said switch contact paths. 
     
     
       6. The invention according to claim 3 wherein each of said plurality of charge conductive paths includes a plurality of charge conductive spikes, each extending from each said conductive path towards a separate one of the switch contact foil pairs of each of said columns of switch contact foil pairs and wherein each of said switch contact paths of each said column has a charge conductive spike extending outwardly therefrom towards the corresponding charge conductive spike on an adjacent one of said of charge conductive paths so as to form a spark gap therebetween to enable an electrostatic discharge to jump said spark gap and to be carried along each said charge conductive path to said ground plane. 
     
     
       7. The invention according to claim 5 wherein each of said switch paths within said matrix array which is located closest to said ground path is provided with a spike path extending outwardly toward said ground plane path and wherein said ground path is provided with a plurality of spike paths, each extending inwardly toward the corresponding spike path associated with each of said switch contact paths located closest to said ground path. 
     
     
       8. A printed circuit board having a metal clad surface which embodies a perimeter ground path foil thereon and at least one switch contact foil pair lying within the area bounded by said perimeter ground path foil wherein the improvement comprises; at least one charge conductive foil embodied on said metal clad substrate surface so as to extend from said ground path foil adjacent to said switch contact foil pair for carrying any electrostatic discharge impacting the printed circuit board adjacent to the switch contact foil pair away from the switch contact foil pair to the ground path foil.   
     
     
       9. The invention according to claim 7 further including: a first conductive spike foil extending from one of the switch contact foil pairs towards said charge conductive foil and a second conductive spike foil extending from said charge conductive foil towards said first conductive spike foil so as to form a spark gap therebetween to enable an electrostatic discharge to jump across said spark gap from said switch contact foil pair so as to be carried along said charge conductive path to the ground plane.